The present invention pertains generally to data recording and recovery methods, and more particularly to a method for logically rejecting previously recorded track residue from magnetic media.
Tape storage technology is routinely used for routine system back up and long-term data archiving. In the ongoing goal to minimize the cost-to-capacity ratio while still maintaining data integrity, ways are always looked at to reduce drive costs. One way to reduce drive costs is to reduce the costs of the components of the recording device. For example, in the tape drive industry, many tape drive architectures employ an erase head for erasing a magnetic tape before recording data to it. In prior art architectures, this is necessary because portions of tracks written onto the tape that are not precisely overwritten may be unintentionally detected by the read head during a later read session. These previously written portions of tracks, herein termed xe2x80x9cresiduexe2x80x9d, are problematic because although they are not intended to be read, they are still detected by the read logic.
Accordingly, a need exists for a method for logically rejecting previously recorded track residue during a read session to prevent data that is not intended to be read from being included in the recovered data sent to the host system.
U.S. Pat. No. 4,910,736 to Tonaka et al. describes the addition of an identification (ID) code and an error check code to each block of the data that makes up a track. The ID code is used to indicate that the block of data belongs to a particular recording session. The error check code is used for error checking of the block of data. In the absence of an error, the original ID code is reconstructed and compared to a reference ID code obtained from a reference ID code setting circuit. If the reconstructed ID code does not match the reference ID code, the block of data is logically rejected as not intended to be read. This approach for logically rejecting residue data reconstructs the original ID code for each block of data recovered from the medium. In addition, a separate reference ID code setting circuit is employed to obtain the reference ID code.
In the interest of reducing the amount of time it takes to determine whether a given block of data belongs to the same recording session as identified by the reference ID code, it would be desirable to have a method for logically rejecting recovered data without having to reconstruct the original ID code for every block of data. In addition, it would be desirable to reduce the amount of hardware, and thus the amount of valuable chip space required to implement the method.
The present invention is a novel method for logically rejecting previously recorded track residue from magnetic media by encoding an identical recording session ID code into the track packet error correction code of every track packet recorded during a single write session. Error correction is performed on the first few track packets to acquire a reference session ID. The reference session ID is used to preload the ECC syndrome and CRC generators prior to processing each recovered packet to determine whether the recovered packet is valid for the current session. Those packets that are recovered but which have a session ID that does not match the acquired session ID are inherently rejected as unintended to be read because the ECC syndromes and CRC generators will indicate an error. As a result, there is no need to actually reconstruct the packet""s original session ID. Accordingly, the invention provides an efficient way of determining whether a recovered track packet was recorded during the recording session identified by the acquired session ID.
In accordance with the invention, a session ID unique to a given recording session is generated at the beginning of the recording session and encoded into an error correction code redundancy field of a track packet. When the track packet is written to tape, the session ID itself is not actually sent to the tape, thereby reducing the amount of overhead data required for each track and increasing the actual data-capacity-to-overhead ratio of the media. During a data recovery session, the session ID encoded in the ECC redundancy field of the track packet is acquired by assuming that the entire contents of the first few track packets are good and performing packet error correction on a number of packets to reconstruct the current session ID. If several consecutively reconstructed session IDs match, the session ID is considered acquired. Once the session ID is acquired, it is preloaded into the CRC/ECC error detection and correction hardware prior to processing each subsequent recovered track packet. Only recovered track packets that are encoded with the acquired session ID are considered good and therefore allowed to be sent to the data buffer; packets that are encoded with a different session ID other than the acquired session ID are rejected by the CRC/ECC error detection and correction hardware.
Accordingly, the technique of the invention eliminates the need for a costly erase head yet requires no additional track packet overhead to be recorded onto the magnetic media. In addition, track packet rejection is more efficient since once the reference session ID is acquired, the original session ID need not be reconstructed for every recovered track packet. Finally, the same error correction hardware used to correct packet errors is used to acquire the session ID, thereby eliminating the requirement for separate hardware to do each function.